For many years museum collections formed our main source of information on bird distributions, especially of the wintering areas of those northern hemisphere birds that migrate to the tropics for the non-breeding season. The aim of skin collectors, operating mainly in the nineteenth century, was to preserve representative samples of all the species occurring in different areas. These specimens still provide invaluable information on the tropical wintering areas of many migrants which have yielded few ring recoveries or observational records. Among European breeding birds, for example, the winter distribution of the Common Cuckoo Cuculus canorus in Africa is still better known from museum skins than from ring recoveries.
Over much of the world, however, increasing information is becoming available on the breeding and non-breeding distributions of birds through the collective efforts of bird-watchers (Chapter 13). For some parts of the world these distributions have been depicted at relatively fine scale in recent 'atlas' projects. However, in most tropical regions, where many high-latitude breeding species spend the non-breeding season, bird distributions are still poorly mapped, despite greater travel by bird-watchers. The main value of such distributional data in our present context, however, is in showing where the same species occur at different times of year; in other words, in revealing breeding and non-breeding ranges, as well as migration routes.
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